Order apps in main screen by date, new, then presence of feature graphic
This is a conservative fix. If we wanted to really highlight the feature graphic functionality and reward upstream devs for keeping metadata up to date, then we could also take apps which were recently updated, and prioritise them over new apps if they have a feature graphic.
Fixes #938 (closed).
Also fixed display of feature graphic in main screen by getting full path to image, not the relative path (e.g. "en-US/featureGraphic.png").